Bulk handling – most common grades of fire resistance
EN 12882 Category 1. EN 12882 contains the standards for electrical and flammability safety requirements for general purpose conveyors used above ground. Category 1 is the most basic classification and simply demands that the belt is anti-static. This means that the belt meets the primary requirement for use in ATEX 114 (Directive 2014/34/EU) classified zones if necessary.
Application: In environments where coal dust, fertilizer, grain or other potentially combustible materials such as biomass are present, it is essential that the conveyor belt cannot create static electricity that could ignite the atmosphere. Belts need to be able to allow static electricity to pass through the metal frame of the conveyor structure down to earth rather than allow static to build up. The safest approach is for all belts to meet EN 12882 Category 1.
EN 12882 Class 2A and Class 2B
The basis of most tests within EN 12882 for belting actual fire resistance is EN ISO 340*. These standards make the distinction between fire resistance with covers, which is Class 2A (often referred to as K grade) and fire resistance with and without covers, which is Class 2B (often referred to as S grade). The relevance of “with and without covers” is primarily because the rubber skim layers between the synthetic plies protect what is essentially the most flammable part in the construction and which can provide the path for flames to propagate. The rubber skim material therefore needs to be as equally fire resistant as the outer covers. Unfortunately, manufacturers who want to minimise costs to achieve a more competitive price often use rubber skims that have insufficient resistance to fire and/or are too thin.
The time it takes for the belt sample to self-extinguish after the flame has been removed is measured. The duration of continued burning (visible flame) should be less than 15 seconds for each sample with a maximum cumulative duration of 45 seconds for each group of six tests. The average allowable time per sample is therefore 7.5 seconds. This factor is crucial because it determines the distance that the fire can be effectively carried by a moving belt. For this reason, Fenner Dunlop in The Netherlands strive for an average maximum time limit of only one second, which is more than six times faster than the required standard.
Application: For the majority of bulk material handling ‘open air’ applications, EN 12882 Class 2A (K grade) or Class 2B (S grade) levels of fire resistance would be perfectly adequate. The best way to decide between Class 2A and Class 2B is to consider the material being carried. For moderately abrasive materials such as grain, then Class 2A is usually suitable. However, if the material is more abrasive and tends to wear the top cover more rapidly and/or you would prefer a higher level of fire safety then the safest option is to choose Class 2B.
EN 12882 Class 4A
Class 4A involves a more severe fire test according to EN 12881-1 method A, C or D in addition to EN ISO 340 testing.
Application: This increased level of fire safety is particularly necessary when conveying biomass because the dry flammable dust found in biomass can be ignited by static electricity created by abrasion within the conveyor system because the source only requires ignition energy as low as 17mJ for ignition to take place. Biomass dust is also prone to self-ignition, especially if it becomes damp. A chemical reaction can take place that causes self-heating and what is referred to as “off-gassing” (carbon dioxide, carbon monoxide and methane emissions).
Although the use of covered conveyors minimizes this risk, the risk to human life is heightened in enclosed environments because burning rubber belts release thick toxic smoke that contains cyanide, carbon monoxide, sulfur dioxide, and products of butadiene and styrene. EN 12882 Class 4A is therefore usually also the best choice for conveyors operating in closed or covered conditions
You cannot put a price on safety.
Experience shows, without doubt, that the price will invariably be reflected in its overall performance including its ability to self-extinguish fire in good time. The low prices may be very tempting, but it is important to understand how those prices are achieved. The true reason is that raw materials, including the expensive chemicals needed to create rubber that has a good standard of resistance to fire, represent up to 70% of the cost of producing a conveyor belt. Consequently, the only way to manufacture a low-price belt is to use (or omit altogether) low grade raw materials and essential additives. There simply is no other way. The price of an insufficiently fire-resistant conveyor belt cannot be calculated. It really is a matter of life and death.
